Voice frequency ringer



I Ja. 21,11947. w, BRANDT 2,414,440

VOICE FREQUENCY RINGER Filed Feb. 2l, 1945 l o QI@ 1f 5;? we

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, WAL TER BMA/0T Patented Jan. 21, 1947 v VOICE FREQUENCY RINGER Walter Brandt, Jersey City, N. J., assgnor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application February 21, 1945, Serial No. 579,126

11 Claims.

This invention relates to signalling as exemplied in voice frequency ringing circuits. It has been found advantageous in various types of cornmunication system to employ an A.C. frequency for ringing or other signalling which lies within an important portion of the voice frequency range. The currents for both voice and signalling traverse the same path to some extent. in

case of carrier systems, it is feasible to make the application of signalling frequency currents at atransmitting point directly to the transmitting branch. In doing so, however, there may be involved in some cases, the disadvantages of providing means for detuning the carrier oscillator in that branch.

An object of the present invention is to provide a signalling system wherein, the case cf two-branch channel terminal between a trunking cnice and a carrier frequency line, the oscillator of the receiving branch is detuned under control of the low frequency signal-control cul'- rent from the oiiice, and the currents of altered frequency are applied over the remaining portion of the receiving branch and thence through the hybrid coil to the transmitting branch and there treated and transmitted in the same manner as voice currents.

Another object is to provide at a receiving point an arrangement for separating signalling or ringing and voice currents as they are received over a common circuit without altering such circuit.

A related object is to (so-ordinate the transmitting and receiving signalling arrangements for proper operation in a two-branch trunking terminal of the type above mentioned.

A further object is to provide a discriminator capable of translating effectively, the signalling current energy in the voice frequency range as received over a common circuitl into a ringing control form and suppressing the effect for that purpose of voice currents received thereover.

Further objects and arbetter understanding of the invention may be derived from the following description of an embodiment thereof taken with the accompanying illustrative drawing.

1n the drawing, Fig. 1 shows diagrammatically one embodiment of my invention as applied to a two-way terminal between a trunk cfce and acarrier line in a. telephone system, and Fig. 2 shows in similar manner a, modified form of the receiving and discriminating portion.

Referring to Fig. 1 of the drawing there is shown a. two-branch terminal which in its general aspects is conventional. To this my invention has been applied in such a, way that-the one direction signalling or ringing `current is transmitted over one branch and in the opposite direction it is received and translated into signal controlling form in the other branch. For the purpose of this invention, it is not necessary to describe the terminal in detail. In the application of my invention, the incoming trunk from an oice, transmits a control signal which, for example may be alternating current of 20 cycles per second. Bridged across this incoming line is an A.C. relay RELI. Contact RII of this relay, controls the continuity of the incoming line at a point on the `terminal side of the bridge. At the demodulator in the receiving branch B, contact RIZ controls the continuity of the primary Winding of the output transformer of this demodulator while contact RI3 controls continuity of the neutral line in the demodulator so that by a change of this contact, a, secondary winding of the transformer, coupling oscillator 2 to the demodulator, is switched from said neutral circuit to the half of the primary winding which is not controlled by RI2. In this way the demodulator is unbalanced and the output of oscillator 2 is applied in series with the said half of the primary of the output transformer. Contact RM of said relay RELI controls a variation of capacitance in the tank circuit of oscillator` 2 so as to alter its frequency to a point where it may be used for producing the modulation in accordance with the desired signalling, for example, in the order of 2500 cycles per second.

The operation of the circuits thus far described I are as follows: Upon the application of the low voltage control current from a 20 cycle oiiicc source to relay RELI, this relay opens its contacts RII to break connection to the office trunk and unbaiance the hybrid coil. It also opens contacts RIZ and switches contacts RIS from back to front, whereby the coupling transformer has its second winding switched to transmit oscillations from oscillator 2 through the output transformer. At contacts RM the frequency of oscillator 2 is changed. Accordingly, oscillations at the desired signal frequency are transmitted through a low pass filter, a receiving amplifier and over transformer TR through the unbalanced hybrid coil and over branch A where they serve to modulate the oscillations from oscillator l in exactly the same manner as voice frequencies produce modulation. This modulated energy is passed along the branch A and out to the high frequency line through the direction filter.V k

The receiving portion of my invention is con- 3 stituted as follows: The output transformer TR has an additional secondary winding. This serves to couple the conventional receiving branch path over contacts RIS of relay RELI to a receiving discriminator arrangement RD. In the form shown in Fig. 1, this arrangement comprises a thermionic tube which as shown is a pentode, although it could be of other yadaptable construction. This tube has the usual biassing parallel arrangement C2-R2 and the control grid is coupled back over the capacitor Cl to said additional secondary winding. The tube is provided with an output circuit which is connected across an additional grid, such as a screen grid, and the anode. Across this circuit is bridged relay REL 2. This circuit is extended also to a network which may be properly termed the discriminator itself. Across this extended circuit is bridged in series connection an L-C loop circuit Li-C5 and a large resistance R3. That portion' of the circuit across the loop is extended via rectiflers, Di, DZ and resistors R4, R in the respective conductors, and across this extension a resistance-capacitance network consisting of resistances Rt, Rl in parallel with capacities Ci, Ci is bridged. The intermediate points of the series capacities andseries resistances are connected to that terminal of R3 remote from the loop circuit. Connection is extended from the high potential point of RB- CS by way of a feed-back circuit through resistor RI to the control grid of tube T.

The operation of the last mentioned circuits is as follows: Assume that an incoming wave traversing the direction filter carries a modulation in the voice range. In normal telephonie transmission it will traverse a band pass lter in branch B and, by the joint operation of oscillator 2 and the demodulator, said'incoming wave will be demodulated and the modulating frequency component will be transmitted through` a low pass filter andra receiving amplier and thence through the hybrid coil and over contacts REI, R22 to the oflice trunk. During this operation it is assumed that none of the contacts of relay RELI have been changed from their normal positions.

Accordingly some of the energy present lat transformer 'IR will pass by way of the additional secondary winding of the receiving dis" criminator RD and be impressed on the control grid of the tube T. In its normal condition, this tube does not pass suflicient plate current to energize Yrelay RELZ. When, however, such incoming waveis constituted essentially by a single frequency signalling wave, some of the energy after demodulation will be impressed on and amplified by the amplifier, and the output therefrom, in turn, will be impressed across the` above described loop-resistance bridge connection. If the L-C circuit, Ll-C5, is tuned tothe frequency of this incoming signalling wave, it offersa high impedance. thereto and energy at this frequency is thereupon rectified in rectier Dl, and the direct current potential is impressed through resistor R4 on the high potential point of the RS-C combination.v From that point it is transmitted by way of the feed-back FB to control grid. In this manner the tube produces'sufcient amplification'A to energize relay PELE. Should, however, the demodulation energy contain waves of other frequencies than the signallingwave, such as those in the usual voice band, a different'operation takes place at the discriminator. In that even-t,the L-C circuit offers only a low impedance while R3 offers a high impedance so that the energyV produced by a resistance drop in R3 is rectified by rectier D2 in a proper direction so that a D.C. potential appearing across the combination R'I-Cl will be of the polarity opposite to that produced in case of the single frequency thereby producing by way of the feed-back a sufficiently negative biassing potential for maintaining relay RELZ inoperative.

In the first assumed case, the demodulated lringing orsingle frequency signal by operating relay REL2 shifts contacts R2l, R22 so as to break the connection of the incoming olce trunk to the hybrid coil and apply low frequency control current to said office trunk for indicating the incoming signalling or ringing operation. It will be noted also that the shifting of contacts R'l, R22 prevents the direct application of the ringing or signalling current itself to the olice trunk line.

In case mixed frequencies in the voice range are impressed on the discriminator a small portion of their energy will be passed by way of rectier DI to the positive terminal of R3, Ct combination. The amount of this energy, however, is small compared to that which will ber passed by rectifier D2. By choosing resistor R4 to be greater than resistor R5 the D.C. voltage developed across said resistor-condenser combination is smaller than the voltage across the R'-C'i combination. It will be seen, therefore, that all the frequencies in the received band other than the particular signallingfrequencies counteract the effect of this particular signalling frequency and that it is only in the absence of such other frequencies that the incoming particular signal frequency can make thegrid sufciently positive to operate relay RELZ. It is to be additionally noted that a desired time delay can be effected by a proper choice of values among the elements R4, R5, R6, Rl, C5 and Cl. Furthermore, the feed-back arrangement offers the advantage of increased sensitivity and reliability in the operation of the discriminator.

In Fig. 2, I have shown a receiver discriminator RD which is modified from that inFig. 1.v This discriminator comprises in general, an amplifying tube A andan input therefor consisting of av terminal by way of transformer TR is like that inV Fig. l. Between its upper two terminals C and D,`

this network has two paths. One comprises a narrowband-pass lter consisting of a series resonant circuit Fl and an anti-resonant circuit F2; the other path comprises an antiresonant circuit F3 and a rectier E so poled as to pass only the negative half waves.` The return circuit of antiresonant loop F3 is by way ofV resistance L, of low value which acts asa lo-ad for said loop circuit F3. The return from the opposite pole of the rectifier is by way of the high resistance M which acts as a D.-C. path for the rectifiedV current and also, along with aV parallel capacity C9, constitutes delay circuit.

The operation of` this modication is as kfollows: Normally, the bias vof tubeY is such that itv does not pass enough plate current to operate .the

relay. If the incoming energy is essentially only that of a particular signalling frequency to which above described narrow band-pass lter without traversing the rectifier and is applied to the grid of the tube in such a way as to materially increase the iiow of plate current and, thereby, operate relay RELZ. In case, however, the incoming en- .ergy is of various frequencies in the voice band,

they are largely transmitted over the second path above described and are rectified by the rectifier E, thereby, producing a D.C. potential at the terminal of resistance M which is so far negative as to prevent the operation of the tube to supply suii'icient plate current for operation of relay RELZ.

What I claim is:

l. Apparatus for transmitting signals in opposite directions over a two branch trunking circuit having hybrid coil connection at one end for low frequency and direction connection at the other end for high frequency and an oscillator for each branch, comprising means responsive to control currents to alter the tuning of the receiving branch oscillator to produce signalling currents of voice frequency, means for transferring said signalling currents to the transmitting branch, means for receiving over the direction connection incoming current energy and for demodulating it under control of the receiving branch oscillator into signals of voice frequency range, and circuit means normally connected to the receiving branch for discriminating between control current and voice frequency signalling currents.

2. Apparatus according to claim 1 wherein said means responsive to said control currents conditions the hybrid coil for transferring said signalf ling currents and disabling the discriminator means.

3. Apparatus according to claim 1 wherein said means responsive to said control currents includes means for unbalancing the demodulator and establishing a path for oscillations from the oscillator to the outgoing end of the receiving branch.

4. A signalling apparatus having a two-branch telephone trunking circuit having an oscillator in a transmitting branch and an oscillator in the receiving branch, means responsive to control currents to alter the tuning of the receiving branch oscillator to produce signalling currents of voice frequency, means for transferring said signal currents to the transmitting branch to control the energy of the transmitting oscillator and means for transmitting said controlled energy.

5. A signalling apparatus according to claim 4 wherein the hybrid coil connects the two branches to the line carrying the incoming control currents, and the responsive means conditions the hybrid coil for said current transferring.

6. A signalling apparatus comprising a line transmitting a band of low frequency alternating currents, a bridge thereacross including in series a loop circuit antiresonant to substantially a single frequency in said band and a resistance, a thermionic relay coupled to said line, means for biassing said relay to control its operation including means for translating thereto differentially the band and the single frequency energies respectively as determined by said bridge..

7. A signalling apparatus according to claim 6 wherein the translating means includes a rectifier for determining the polarity of the biassing means.

8. A signalling apparatus comprising a line transmitting a band of low frequency alternating currents coupled to the input of a thermionic re-v lay, an output circuit for said relay, a bridge thereacross including in series a loop circuit antiresonant to substantially a single frequency in said band and a resistance, means for reotifying selectively the low frequency energies across the anti-resonant loop and resistance, and means for combining their direct current products to bias the tube for selective operation.

9. Apparatus according to claim 8 having means for differentially combining the direct current energies.

10. A signalling apparatus comprising a line transmitting a band of low frequency alternating currents, a frequency discriminating network comprising a band lter passing substantially only a single frequency with further means for passing with little attenuation frequencies.` of said rst mentioned band other than said single frequency, said network including means for deriving from said frequencies a direct current potential, a thermionic relay connected to said network and means for selectively controlling operation of the thermionic relay in accordance with the output energy of said filter and said further means.

11. Apparatus according to claim 10 wherein the network includes an impedance bridge across said line having in series a loop anti-resonant to said single frequency and a resistance.

WALTER BRANDT. 

